Critical Reasoning

richachampion wrote:Frobisher, a sixteenth-century English explorer, had soil samples from Canada's Kodlunarn Island examined for gold content. Because high gold content was reported, Elizabeth I funded two mining expeditions. Neither expedition found any gold there. Modern analysis of the island's soil indicates a very low gold content. Thus the methods used to determine the gold content of Frobisher's samples must have been inaccurate.

Which of the following is an assumption on which the argument depends?

A. The gold content of the soil on Kodlunarn Island is much lower today than it was in the sixteenth century.
B. The two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn Island.
C. The methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.
D. Frobisher did not have soil samples from any other Canadian island examined for gold content.
E. Gold was not added to the soil samples collected by Frobisher before the samples were examined.

NandishSS wrote:

GMATGuruNY wrote:

richachampion wrote:Frobisher, a sixteenth-century English explorer, had soil samples from Canada's Kodlunarn Island examined for gold content. Because high gold content was reported, Elizabeth I funded two mining expeditions. Neither expedition found any gold there. Modern analysis of the island's soil indicates a very low gold content. Thus the methods used to determine the gold content of Frobisher's samples must have been inaccurate.

Which of the following is an assumption on which the argument depends?

A. The gold content of the soil on Kodlunarn Island is much lower today than it was in the sixteenth century.
B. The two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn Island.
C. The methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.
D. Frobisher did not have soil samples from any other Canadian island examined for gold content.
E. Gold was not added to the soil samples collected by Frobisher before the samples were examined.

Premise:
In the 16th century, an examination of Frobisher's soil samples from Kodlunarn Island indicated high gold content, but a modern examination of soil samples from this island indicate very low gold content.
Conclusion:
The methods used to determine the gold content of Frobisher's samples must have been inaccurate.

Apply the negation test.
When the correct answer choice is negated, the conclusion will be invalidated.

E, negated:
Gold was added to the soil samples collected by Frobisher before the samples were examined.
Thus, the 16th-century methods that detected gold were ACCURATE:
They detected a high gold content because gold had been ADDED to the samples.
Since the negation of E invalidates the conclusion that the 16th-century methods were inaccurate, E is an assumption: a statement that MUST BE TRUE for the conclusion to hold.

The correct answer is E.

HI Mitch,

If you negate A -- The gold content of the soil on Kodlunarn Island is not much lower today than it was in the sixteenth century
it means the gold content is higher now the methods used to determine the gold content of Frobisher's samples cannot be inaccurate.

I'm convinced that E is correct ans but, how you eliminate A?

Thanks
Nandish